One way to help make the transition from basic facts to "big" multiplication easier is by taking it step by step. One of those steps is learning how to multiply by multiples of tens, hundreds, and even thousands. Over the years I have developed, with the help of some students, an easy way to teach this concept.
The first step is to circle the basic fact. EX: 40 x 6= The basic fact is 4 x 6. Once you know the basic fact-4 x 6=24, then just count the zeroes and add them to the basic fact-24 + 1 zero=240.
My students even helped me make up a song to help students remember the steps:
He just won't stop!
All you do is count him,
At the top!
You add those zeroes,
To the basic fact,
And you will get the answer,
Just like THAT!
We use Zero the Hero to help us any time we are multiplying by multiples of tens and hundreds. It comes in really handy when multiplying with partial products and estimating.
I have a fabulous PowerPoint presentation that takes students through multiplying by multiples of tens and hundreds step by step. It even includes the song with me singing :) It provides examples, activities, and test practice.
Check it out at my TpT store.
Here are some of the videos and games that I embed into my presentations: